As integrated circuits (ICs) and micro-fabrication technologies develop rapidly, new materials, processes, and devices are emerging in recent years. Among them, new materials are more attractive. For example, two-dimensional crystal materials, such as graphene, transitional metal disulfides, and germylene, are always being focused on since the advent thereof, due to their excellent properties.
However, those two-dimensional crystal materials encounter various problems, such as contact resistance between them and other materials. It is desirable to reduce the contact resistance to access their excellent electrical properties. For example, the graphene can be used as a channel material for transistors, due to its ultra-high carrier, mobility at room temperature. However, the contact resistance between graphene and other materials hinders further progress in device performance. Long-channel devices may have relatively high tolerance to contact resistance, but the performance of short-channel devices will be suppressed greatly if the contact resistance is comparable to the channel resistance. The contact resistance between the graphene and other materials has become a bottleneck, which prevents graphene-based devices from scaling down and enhancing performance.